Implantable pulse generator and method having adjustable signal blanking

ABSTRACT

An implantable pulse generator senses a cardiac signal, identifies cardiac events in the cardiac signal, and starts a blanking interval including a repeatable noise window blanking interval in response to each cardiac event. When noise is detected during the repeatable noise window blanking interval, the noise window blanking interval is repeated. In one embodiment, the duration of repeated repeatable noise window blanking intervals is summed and compared to a pacing escape interval. When the sum is greater than the pacing escape interval, asynchronous pacing pulses are delivered until the noise ceases. Alternatively, when the sum is greater than the pacing escape interval, the pace escape interval is repeated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/889,348,filed on Jul. 12, 2004, which is a continuation of application Ser. No.09/650,913, filed on Aug. 29, 2000, now issued as U.S. Pat. No.6,873,875, the specifications of which are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present invention concerns implantable medical devices, and moreparticularly concerns implantable pulse generators having adjustablesignal blanking intervals.

BACKGROUND

When functioning properly, the human heart maintains its own intrinsicrhythm, and is capable of pumping adequate blood throughout the body'scirculatory system. However, some people have irregular cardiac rhythms,referred to as cardiac arrhythmias. Such arrhythmias result indiminished blood circulation. One mode of treating cardiac arrhythmiasincludes the use of an implantable pulse generator. An implantable pulsegenerator is implanted in the patient and delivers therapy to thepatient's heart under certain predetermined conditions.

An implantable pulse generator can be, among other things, a pacemaker.A pacemaker delivers timed sequences of low energy electrical stimuli,called pace pulses, to the heart, such as via an intravascular lead(referred to as a “lead”) having one or more electrodes disposed in orabout the heart. Heart contractions are initiated in response to suchpace pulses (this is referred to as “capturing” the heart). By properlytiming the delivery of pace pulses, the heart can be induced to contractin proper rhythm, greatly improving its efficiency as a pump. Apacemaker is often used to treat patients with bradyarrhythmias, thatis, hearts that beat too slowly, or irregularly.

An implantable pulse generator can also be a cardioverter/defibrillator.A cardioverter/defibrillator is capable of delivering higher energyelectrical stimuli to the heart. The cardioverter/defibrillator is oftenused to treat a patient with a tachyarrhythmia, that is, a heart thatbeat too quickly. Such too-fast heart rhythms also cause diminishedblood circulation because the heart isn't allowed sufficient time tofill with blood before contracting to expel the blood. Such pumping bythe heart is inefficient. A cardioverter/defibrillator is capable ofdelivering a high energy electrical stimulus that is sometimes referredto as a defibrillation countershock. The countershock interrupts thetachyarrhythmia, allowing the heart to reestablish a normal rhythm forthe efficient pumping of blood. In addition to the pacemaker and thecardioverter/defibrillator, an implantable pulse generator can combinethe function of the pacemaker and the cardioverter/defibrillator, drugdelivery devices, and any other implantable or external systems ordevices for diagnosing or treating cardiac arrhythmias.

A typical pacemaker and/or cardioverter/defibrillator include one ormore electrical leads, which extend from a sealed housing of the pulsegenerator through the venous system into the inner walls of a heart.Within the housing are a battery for supplying power, a capacitor fordelivering bursts of electric current through the leads to the heart,and monitoring circuitry for monitoring the heart and determining notonly when and where to apply the current bursts but also their numberand magnitude. The monitoring circuitry generally includes amicroprocessor and a memory that stores instructions directing themicroprocessor to interpret electrical signals that naturally occur inthe heart as normal or abnormal rhythms. For abnormal rhythms, theinstructions, or more generally signal-processing algorithm, tell theprocessor what, if any, electrical therapy should be given to restorenormal heart function.

In general, these algorithms use the time intervals between successiveheart beats, or cardiac events, as key determinants of therapydecisions. Thus, to ensure the validity of therapy decisions, it is veryimportant to ensure accuracy of these intervals. Determining theseintervals can be especially problematic in a dual-chamber pacemakerand/or cardioverter/defibrillator. In the dual chamber device, a cardiacsignal is monitored from two chambers of the heart, such as the rightventricle and the right atrium. In this device, there is a significantrisk of mistaking a ventricle beat for an atrial beat, and thereforecounting too many atrial beats and miscalculating some atrial intervals(the time between atrial beats).

In addition to mistaking sensed signals from cardiac chambers, “noise”from non-cardiac sources can also be problematic for the pacemakerand/or cardioverter/defibrillator. Noise interferes with the properoperation of the device, and is most commonly caused by externalelectrical interference. The response of the implanted device in thepresence of noise, or interference, is important in ensuring the deviceis ready to provide therapy to the patient regardless of the presence ofnoise.

Thus, there is a need in the art for effective ways of addressing noisesensed in cardiac signals sensed by an implanted pulse generator, andmaintaining a proper response of the implantable pulse generator in thepresence of such noise.

SUMMARY OF THE INVENTION

The present subject matter provides an implantable pulse generator and amethod of its operation that fulfills the aforementioned needs, alongwith other needs in the art. The implantable pulse generator initiates ablanking window during sensed cardiac signals in response to certainpredetermined conditions. These conditions include a sensed cardiacevent and/or a paced cardiac event. The blanking window includes arepeatable portion that is triggered by noise sensed in the cardiacsignal. When triggered, the repeatable portion of the blanking windowextends blanking window, thus preventing noise from being included inthe analysis of and response to the sensed cardiac signals.

In an exemplary embodiment, the implantable pulse generator includes afirst cardiac lead having one or more electrodes, where the one or moreelectrodes are coupled to a signal sensor to sense a first cardiacsignal. The pulse generator further includes a blanking window initiatorcoupled to the signal sensor. The blanking window initiator identifiescardiac events, sensed or paced, in the first cardiac signal and startsa blanking interval in response to an identified cardiac event. Theblanking window is an interval of time during which a sensed cardiacsignal is ignored by the implantable pulse generator.

The blanking interval further includes a repeatable noise windowblanking interval. The repeatable noise window blanking interval is aportion of the blanking interval that is repeated if noise is detectedin the sensed cardiac signal during the repeatable noise window. In oneembodiment, noise includes sensed signals having a predeterminedfrequency range.

A noise detector is further coupled to the signal sensor and theblanking window initiator. In one embodiment, the noise detectoranalyzes the first cardiac signal to detect noise in the first signal.When noise is detected in the first signal during the repeatable noisewindow blanking interval portion of the blanking window, the blankingwindow initiator repeats the repeatable noise window blanking interval.

When the repeatable noise window blanking interval is being repeated,the noise detector sums a duration of repeated repeatable noise windowblanking intervals. When the sum of the duration of the repeated noisewindow blanking becomes greater than a pacing escape interval, the noisedetector issues a first signal to start delivery of asynchronous pacingpulses. When the noise signal ceases or is no longer detected, the noisedetector issues a second signal to stop delivery of asynchronous pacingpulses.

In an alternative embodiment, the noise detector sums repeated noisewindow blanking intervals to give a duration of the repeatable noisewindow blanking intervals. This value is then compared to the pacingescape interval. When the duration of the repeatable noise windowblanking intervals is greater than the pacing escape interval, the noisedetector repeats the pace escape interval. Once the noise ceases, thenoise detector issues a first signal to resume pacing after one pacingescape interval.

In an additional embodiment, the implantable pulse generator furtherincludes a second cardiac lead having one or more electrodes that areused to sense a second cardiac signal. When two cardiac signals aresensed (e.g., the first cardiac signal and the second cardiac signal),which cardiac signal is blanked (i.e., sensed but the signal is ignoredby the implantable pulse generator) depends upon where the cardiacsignals are being sensed from the heart and what type of cardiac complexis being sensed. For example, when the first cardiac signal is an atrialsignal and the second cardiac signal is a ventricular signal, a sensedatrial contraction in the atrial signal initiates the blanking intervalin the ventricular signal. Similarly, when the first cardiac signal isthe ventricular signal and the second cardiac signal is the atrialsignal, a sensed ventricular contraction in the ventricular signalinitiates the blanking interval in the atrial signal.

In a further embodiment, the duration of the blanking interval alsodepends upon the type of cardiac event sensed in the cardiac signal. Forexample, the blanking window initiator identifies cardiac events aseither sensed intrinsic cardiac events or paced cardiac events. Based onthe identification of the sensed cardiac complex, the blanking windowinitiator adjusts the blanking interval to a first overall duration whena paced cardiac event is identified and to a second overall durationwhen a sensed cardiac event is identified.

These and other embodiments, aspects, advantages, and features will beset forth in part in the description which follows, and in part willbecome apparent to those skilled in the art by reference to thefollowing description of the invention and referenced drawings or bypractice of the invention. The aspects, advantages, and features of theinvention are realized and attained by means of the instrumentalities,procedures, and combinations particularly pointed out in the appended

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart illustrating an exemplary method of thepresent subject matter;

FIG. 2 is schematic of a blanking interval according to an exemplaryembodiment of the present subject matter;

FIG. 3 shows a flow chart illustrating an exemplary method of thepresent subject matter;

FIGS. 4A and 4B are schematics of a blanking interval according toexemplary embodiments of the present subject matter;

FIG. 5 shows a flow chart illustrating an exemplary method of thepresent subject matter;

FIG. 6 shows a flow chart illustrating an exemplary method of thepresent subject matter;

FIG. 7 shows a flow chart illustrating an exemplary method of thepresent subject matter;

FIG. 8 shows a perspective view of an exemplary embodiment of animplantable pulse generator partially implanted in a heart from whichsegments have been removed to show detail;

FIG. 9 shows a perspective view of an exemplary embodiment of animplantable pulse generator partially implanted in a heart from whichsegments have been removed to show detail; and

FIG. 10 shows an exemplary embodiment of a block diagram of animplantable pulse generator.

DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that structuralchanges may be made without departing from the scope of the presentinvention. Therefore, the following detailed description is not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims and their equivalents.

FIG. 1 shows a flow chart 100, illustrating an exemplary method of thepresent subject matter. At 110, a first cardiac signal is sensed. In oneembodiment, the first cardiac signal is sensed from any number oflocations on or within the heart. For example, the first cardiac signalis sensed from a right ventricular location, or from a right atriumlocation. Alternatively, the first cardiac signal is sensed from acardiac region that is adjacent to either the left atrium or the leftventricle. The cardiac signal can also be sensed from a cardiac regionthat is between these two regions of the heart. In an additionalembodiment, the first cardiac signal is either a far field signal, alsoreferred to as a morphology signal, or a near field signal, alsoreferred to as a rate signal. Electrode structures and leadconfigurations with these electrodes are known.

At 120, as the first cardiac signal is sensed, cardiac events aredetected and identified in the first cardiac signal. In one embodiment,the cardiac events are identified by analyzing the cardiac signal forcomplexes that exceed a dynamic threshold value, as is known. When acardiac event is detected, a blanking interval is started at 130. In oneembodiment, the blanking interval is a time interval during whichsensing of the cardiac signal is suspended, and therefore, theinformation contained in the cardiac signal during this interval isignored. Blanking intervals are applied in implantable pulse generatorshaving electrodes implanted in only a single chamber. Alternatively,when the blanking interval is used with a dual-chamber pulse generator(e.g., electrodes in two or more chambers of the heart), the blankinginterval is intended to prevent the inappropriate detection of signalsfrom an opposite chamber, commonly referred to as crosstalk.

The blanking interval started when the cardiac event is identified inthe first cardiac signal at 130 further includes a repeatable noisewindow blanking interval. The repeatable noise window blanking intervalis a portion of the blanking interval that is repeatable orretriggerable when noise is detected in the sensed cardiac signal.During this interval, the first cardiac signal is sensed or monitoredfor the presence of noise, or interference. At 140 the first cardiacsignal is analyzed to detect noise in the first cardiac signal duringthe repeatable noise window blanking interval. At 150, when noise is notdetected in the first cardiac signal during the repeatable noise windowblanking interval, the blanking interval ends after expiring and returnsto 110. The blanking interval is then begun again when the next cardiacevent is detected.

When noise is detected during the repeatable noise window blankinginterval at 150, the repeatable noise window blanking interval isrepeated at 160. In one embodiment, the noise window blanking intervalis immediately repeated once the noise is detected. Upon repeating thenoise window blanking interval, the system returns to 140 to analyze thefirst cardiac signal for noise during the repeated noise window blankinginterval, and proceeds through 150 and 160, if necessary, as previouslydescribed.

FIG. 2 is an exemplary embodiment showing the blanking interval 200. Theblanking interval is shown with an absolute blanking period (duringwhich all signals, regardless of origin, are ignored) followed by therepeatable noise window blanking interval 210, during which the firstcardiac signal is monitored for noise signals having predeterminedcharacteristics. In one embodiment, noise is identified as a signalhaving a predetermined frequency range, where the predeterminedfrequency range is a programmable value of greater than 50 Hz.

In addition, a cardiac signal 220 having a cardiac event 230 is shown inrelation with the blanking interval 200. When the cardiac event 230 isdetected the blanking interval 200 is started, as shown by the dashedline 240. During the duration of the blanking interval 200, sensing ofthe cardiac signal 220 is suspended, except for during the repeatablenoise window blanking interval 210.

In one embodiment, the duration of the blanking period is either aprogrammable value or a set value. Which blanking period duration isused depends upon what type of initiator was used to produce the cardiaccomplex sensed in the first cardiac signal. For example, when thecardiac complex detected in the first cardiac signal is a paced cardiaccomplex (i.e., a pacing pulse is used to cause the heart to contract)the duration of the blanking interval is a programmable value in therange of 150 to 500 milliseconds. Alternatively, when the cardiaccomplex detected in the first cardiac signal is an intrinsic cardiacpulse (i.e., contraction started by the heart) the duration of theblanking interval is a set value of 135 milliseconds. The repeatablenoise window blanking is a constant interval set at 40 milliseconds.

FIG. 3 shows a flow chart 300, illustrating an exemplary methodselecting the duration of the blanking period based on the nature of thesensed cardiac complex. The flow chart of FIG. 3 includes blocksdescribed for FIG. 1 that will be briefly described. At 110, the firstcardiac signal is sensed and cardiac events are detected and identifiedin the first cardiac signal at 120, as previously described. At 310, thesensed cardiac event is further identified as either a sensed cardiacevent or a paced cardiac event. In one embodiment, a paced cardiac eventis identified by the system delivering the pacing pulse, as the pacedcardiac event occurs after the pacing pulse is delivered. When the pacedcardiac event is identified, the duration of the blanking interval isadjusted to a first overall duration at 320. In one embodiment, thefirst overall duration is programmable value in the range of 150 to 500milliseconds, as previously described. At 330, when the sensed cardiacevent is identified as an intrinsic cardiac event, the duration blankinginterval is adjusted to a second overall duration. In one embodiment,the second overall duration is a preset value of 135 milliseconds, aspreviously described.

As previously described, the blanking interval further includes therepeatable noise window blanking interval. The repeatable noise windowblanking interval is positioned at a variety of locations along theblanking interval. The location of the noise window blanking intervaldepends upon which type of cardiac event is detected. For example, for apaced event the repeatable noise window blanking interval endsconcurrently with the first overall duration of the blanking interval.

Alternatively, for a sensed intrinsic cardiac event the repeatable noisewindow blanking interval is adjustably programmed to start at any numberof locations during the second overall duration of the blankinginterval. In this embodiment, the second overall duration includes afirst timed interval. The first timed interval is a programmable valueand is an absolute blanking interval. The repeatable noise windowblanking interval is then started after the first timed interval of thesecond overall duration. The repeatable noise window blanking intervalthen runs until it expires, where it is possible that a second timedinterval could occur after the repeatable noise window blanking intervalexpires.

FIGS. 4A and 4B show exemplary embodiments of adjusting the duration ofthe blanking period and the position of the repeatable noise windowblanking interval based on the nature of the sensed cardiac complex. InFIG. 4A, there is shown a blanking interval 400 having an absoluteblanking interval 410. The absolute blanking interval 410 is followed bythe repeatable noise window blanking interval 420. FIG. 4A also shows acardiac signal 430 with a paced cardiac event 440 is shown in relationwith the blanking interval 400. When the paced cardiac event 440 isdetected, the blanking interval 400 is started, as shown by the dashedline 450. During the duration of the blanking interval 400, sensing ofthe cardiac signal 430 is suspended, except for during the repeatablenoise window blanking interval 420. As previously discussed, theduration of the blanking interval 400, which includes the repeatablenoise window blanking interval 420, is a programmable value. Therepeatable noise window blanking interval 420 also expires at the sametime the blanking interval 400 expires, provided noise is not sensedduring the repeatable noise window blanking interval 420. The repeatablenoise window blanking interval is 40 milliseconds, as previouslydescribed.

In FIG. 4B, there is shown a blanking interval 460 that includes arepeatable noise window blanking interval 464. In contrast to FIG. 4A,the position of the repeatable noise window blanking interval 464 alongthe blanking interval 460 is adjustably programmed to start at anynumber of locations during the second overall duration of the blankinginterval 420. The second overall duration of the blanking interval 460includes a first timed interval 470 that is a programmable value in therange of 5 to 45 milliseconds.

The first timed interval is an absolute blanking interval and isfollowed by the repeatable noise window blanking interval 464. After therepeatable noise window blanking interval 464 expires, a second timedinterval 480 begins. In one embodiment, the second timed interval 480 isan absolute refractory period. The duration of the second timed interval480 is determined when the first timed interval 470 is set, as theduration of the repeatable noise window blanking interval 464 is a setvalue at 40 milliseconds. FIG. 4B also shows a cardiac signal 484 with asensed cardiac event 490 is shown in relation with the blanking interval460. When the sensed cardiac event 490 is detected, the blankinginterval 460 is started, as shown by the dashed line 494. During theduration of the blanking interval 460, sensing of the cardiac signal 484is suspended, except for during the repeatable noise window blankinginterval 464.

FIG. 5 shows a flow chart 500, illustrating an exemplary method of thepresent subject matter, where the encircled A and the encircled Bconnect to the corresponding encircled A and encircled B in either FIG.1 or FIG. 3. Blocks 140, 150 and 160 are as previously described, exceptthe method does not return to 140 after 160. After 160, the systemproceeds to 510, where the sum of the repeated noise window blankingintervals is determined. At 520, the sum of the repeated noise windowblanking intervals is then compared to a pacing escape interval todetermine if the sum is greater than a pacing escape interval. In oneembodiment, the pacing escape interval is the period between thedetected cardiac event (sensed or paced) and the next cardiac event(sensed or paced). In one embodiment, the duration of the pacing escapeinterval is a programmable value in the range of 2000 to 342milliseconds.

At 530, when the sum of the repeated noise window intervals is greaterthan the pacing escape interval, asynchronous pacing pulses aredelivered to the heart. At 540, the system determines when the sensednoise has ceased. When the noise has not ceased, the system returns to530. Alternatively, when the noise does cease, the system proceeds to550, where the asynchronous pacing pulses are then stopped. The systemthen returns to sensing the first cardiac signal at 110.

FIG. 6 shows a flow chart 600, illustrating an additional exemplarymethod of the present subject matter, where the encircled A and theencircled B connect to the corresponding encircled A and encircled B ineither FIG. 1 or FIG. 3. Blocks 140, 150 and 160 are as previouslydescribed, except the method does not return to 140 after 160. After160, the system proceeds to 510, where the sum of the repeated noisewindow blanking intervals is determined. At 520, the sum of the repeatednoise window blanking intervals is then compared to a pacing escapeinterval to determine if the sum is greater than a pacing escapeinterval, as previously described. At 610, when the sum of the repeatednoise window intervals is greater than the pacing escape interval, thepacing escape interval is repeated. At 620, the system determines whenthe sensed noise has ceased. If the noise has not ceased, the systemreturns to 140. If the noise has ceased, the system proceeds to 630where the pacing is resumed after the pacing escape interval expires.The system then returns to sensing the first cardiac signal at 110.

FIG. 7 shows a flow chart 700, illustrating an additional exemplarymethod of the present subject matter. At 710, a first cardiac signal anda second cardiac signal are sensed. In one embodiment, the first cardiacsignal and the second cardiac signal are sensed from different cardiacregions. For example, the first cardiac signal is a ventricular signalsensed from a right ventricular location or a location adjacent a leftventricular location and the second cardiac signal is an atrial signalsensed from a right atrium location or a location adjacent a leftatrium. Alternatively, the first cardiac signal is an atrial signalsensed from a right atrium location or a location adjacent a left atriumlocation and the second cardiac signal is a ventricular signal sensedfrom a right ventricle location or a location adjacent a left ventricle.The first and second cardiac signals are each either a near field signalor a far field signal, as previously described.

At 720, as the first cardiac signal is sensed, cardiac events aredetected and identified in the first cardiac signal. When the cardiacevent is detected in the first cardiac signal, a blanking interval isstarted at 730 in the first and second cardiac signals so as to preventthe inappropriate detection of signals from an opposite chamber. In oneembodiment, the atrial signal is sensed for the first cardiac signal andthe ventricular signal is sensed for the second cardiac signal, where anatrial contraction in the atrial signal is identified as the cardiacevent and both the ventricular signal and atrial signal are blankedduring the blanking interval. In an alternative embodiment, theventricular signal is sensed for the first cardiac signal and the atrialsignal is sensed for the second cardiac signal, where a ventricularcontraction in the ventricular signal is identified as the cardiac eventand both the ventricular signal and atrial signal are blanked during theblanking interval.

At 740 both the first cardiac signal and the second cardiac signal areanalyzed to detect noise during the repeatable noise window blankinginterval. At 750, when noise is not detected in the cardiac signalsduring the repeatable noise window blanking interval, the blankinginterval ends after expiring and returns to 710. The blanking intervalis then begun again when the next cardiac event is detected. When noiseis detected during the repeatable noise window blanking interval at 750,the repeatable noise window blanking interval is repeated at 760. Uponrepeating the noise window blanking interval, the system returns to 740to analyze the cardiac signals for noise during the repeated noisewindow blanking interval, and proceeds through 750 and 760, ifnecessary, as previously described. The subject matter described forFIGS. 3, 5 and 6 can also be extended to include an analysis andutilization of both the first and the second cardiac signal.

FIG. 8 shows an exemplary embodiment of a pulse generator 800. The pulsegenerator 800 includes a first cardiac lead 802 having one or moreelectrodes. In one embodiment, the first cardiac lead 802 is aventricular lead adapted to be implanted within a heart 804. The firstcardiac lead 802 includes at least a sense/pace electrode 806, a firstdefibrillation electrode 808 and a second defibrillation electrode 810.FIG. 8 shows an embodiment in which the sense/pace electrode 806 is atip electrode located at the distal end of lead 802 and the first andsecond defibrillation electrodes are coil electrodes.

The first cardiac lead 802 is releasably coupled to the implantablepulse generator 800 so as to couple electrodes 806, 808 and 810 to theelectronic circuitry within the pulse generator 800. This allows forcardiac signals to be sense from and electrical energy pulses to bedelivered to the heart 804. In one embodiment, a first cardiac signal,as previously described, is sensed between the sense/pace electrode 806and the first defibrillation electrode 808. Additionally, a secondcardiac signal, as previously described can be sensed between either thefirst defibrillation electrode 808 and the second defibrillationelectrode 810 or between the a second defibrillation electrode 810 andthe housing 812 of the implantable pulse generator 800. A medical deviceprogrammer 820 is also shown in FIG. 8, where the medical deviceprogrammer 820 and the electronic circuitry within the implantable pulsegenerator 800 are adapted to establish a communication link so as toallow for transfer of data and instructions to and from the devices. Inone embodiment, communication between the medical device programmer 820and the implantable pulse generator 800 is established over a radiofrequency telemetry channel as is known in the art.

FIG. 9 shows an additional exemplary embodiment of a pulse generator900. The implantable pulse generator 900 includes a first cardiac lead902 having one or more electrodes and a second cardiac lead 904 havingone or more electrodes. In one embodiment, the first cardiac lead 902 isa ventricular lead adapted to be implanted within a heart 906. The firstcardiac lead 902 includes at least a sense/pace electrode 908, a firstdefibrillation electrode 910 and a second defibrillation electrode 912.FIG. 9 shows an embodiment in which the sense/pace electrode 908 is atip electrode located at the distal end of lead 902 and the first andsecond defibrillation electrodes are coil electrodes. The second cardiaclead 904 includes a first electrode 914 and a second electrode 915,where the first electrode 914 is shown positioned at the distal end ofthe second lead 904 and the second electrode 915 is shown positionedproximal the first electrode 914 along the second cardiac lead 904.

The first cardiac lead 902 and the second cardiac lead 904 arereleasably coupled to the implantable pulse generator 900 so as tocouple electrodes 908, 910, 912, 914 and 914 to the electronic circuitrywithin the pulse generator 900. This allows for cardiac signals to besensed from and for electrical energy pulses to be delivered to theheart 906. In the present embodiment, a first cardiac signal is sensedbetween the first electrode 914 and the second electrode 915.Alternatively, the first cardiac signal is sensed between either thefirst and/or second electrode 914, 915 and an electrically conductiveportion of the implantable cardiac defibrillator housing 916. A secondcardiac signal is sensed between the sense/pace electrode 908 and thefirst defibrillation electrode 910. Additionally, a second cardiacsignal can be sensed between the first defibrillation electrode 910 andthe second defibrillation electrode 912. A medical device programmer 920is also shown in FIG. 9, where the medical device programmer 920 and theelectronic circuitry within the implantable pulse generator 900 areadapted to establish a communication link so as to allow for transfer ofdata and instructions to and from the devices. In one embodiment,communication between the medical device programmer 920 and theimplantable pulse generator 900 is established over a radio frequencytelemetry channel as is known in the art.

FIG. 10 shows an exemplary embodiment of a block diagram of animplantable pulse generator 1000. The implantable pulse generator 1000includes control circuitry 1002 which receives one or more cardiacsignals and delivers electrical energy to electrodes positioned on theatrial and/or ventricular leads under predetermined conditions. In oneembodiment, the control circuitry 1002 is a programmablemicroprocessor-based system, with a microprocessor 1004 and a memorycircuit 1006, which contains parameters for various pacing and sensingmodes and stores data indicative of cardiac signals received by thecontrol circuitry 1002. The control circuitry 1002 includes terminalslabeled with reference numbers 1008, 1010, 1012, 1014 and 1016 forconnection to the electrodes attached to the surface of a first andsecond lead. In the embodiment shown in FIG. 9, the sense/pace electrode908 is coupled to terminal 1008 through a first electrically insulatedconductor provided within the first lead 902. The first defibrillationelectrode 910 is coupled to terminals 1010 and 1012 through a secondelectrically insulated conductor provided within the first lead 904. Thesecond defibrillation electrode 912 is coupled to terminal 1014 througha third electrically insulated conductor provided within the first lead904. Finally, the first electrode 914 and the second electrode 915 arecoupled to terminals 1016 and 1018, respectively by electricallyinsulated conductors provided within the second lead 904.

The control circuitry 1002 is encased and hermetically sealed in ahousing 1020 suitable for implanting in a human body. In one embodiment,the housing 1020 is made of titanium, however, other biocompatiblehousing materials as are known in the art may be used. A connector block1024 is additionally attached to the housing 1020 to allow for thephysical and the electrical attachment of the leads 902 and 904 and theelectrodes to the implantable pulse generator 1000 and the encasedcontrol circuitry 1002.

Sense amplifiers 1026, 1028 and 1030 are coupled to the controlcircuitry 1002, and are electrically coupled to terminals 1008, 1010,1012, 1014 1016 and 1018 to allow for at least a first cardiac signaland a second cardiac signal to be sensed, as previously described. Theoutput of the sense amplifiers 1026, 1028 and 1030 are connected to asignal sensor 1032 to allow for the first and second cardiac signals tobe sensed and analyzed according to the present subject matter. Ablanking window initiator 1040 is coupled to the signal sensor, wherethe blanking window initiator 1040 identifies cardiac events in eitherthe first cardiac signal or the second cardiac signal, as previouslydescribed. In one embodiment, the blanking window initiator 1040 startsthe blanking interval when the cardiac event is identified in either thefirst cardiac signal or the second cardiac signal, as previouslydescribed.

A noise detector 1044 is coupled to the signal sensor 1032 and theblanking window initiator 1040, where the noise detector 1044 analyzesthe first cardiac signal and the second cardiac signal to detect noisein either the first signal and/or the second signal during therepeatable noise window blanking interval, as previously described,where the blanking window initiator 1040 repeats the repeatable noisewindow blanking interval when the noise detector 1044 detects noise ineither the first signal or the second signal during the noise windowblanking interval.

In an additional embodiment, the blanking window initiator 1040identifies sensed cardiac events and paced cardiac events. The blankingwindow initiator 1040 then adjusts the blanking interval to a firstoverall duration when a paced cardiac event is identified and to asecond overall duration when a sensed cardiac event is identified, aspreviously discussed.

In a further embodiment, the noise detector 1044 sums the duration ofrepeated repeatable noise window blanking intervals. The noise detector1044 then issues a first signal to start delivery of asynchronous pacingpulses when the duration of repeated repeatable noise window blankingintervals is greater than a pacing escape interval. Control circuitry1002 includes a pace output 1050 and a defibrillation output 1054 fordelivering pacing, cardioversion and/or defibrillation pulses throughthe electrodes, where the pace and defibrillation output 1050 and 1054are both under the control of the microprocessor 1004. Power to theimplantable pulse generator 1000 is supplied by an electrochemicalbattery 1060 that is housed within the pulse generator 1000. When thenoise signal is no longer detected, the noise detector 1044 issues asecond signal to stop delivery of asynchronous pacing pulses.

In an alternative embodiment, the noise detector 1044 sums repeatedrepeatable noise window blanking intervals to give a duration of therepeatable noise window blanking intervals. The noise detector 1044compares the duration of the repeatable noise window blanking intervalsto a pacing escape interval. The noise detector 1044 then repeats thepace escape interval when the duration of the repeatable noise windowblanking intervals is greater than the pacing escape interval. When thenoise signal is no longer detected, the noise detector 1044 issues afirst signal to resume pacing after one pacing escape interval after thenoise signal ceases, as previously discussed.

The blanking window initiator 1040 can blank one of both the firstcardiac signal and/or the second cardiac signal, as previouslydiscussed. In one embodiment, when the first cardiac signal is an atrialsignal and the second cardiac signal is a ventricular signal, theblanking window initiator 1040 identifies the cardiac event as an atrialcontraction in the atrial signal. Alternatively, when the first cardiacsignal is a ventricular signal and the second cardiac signal is anatrial signal, the blanking window initiator 1040 identifies the cardiacevent as a ventricular contraction in the ventricular signal.

Electronic communication circuitry 1070 is additionally coupled to thecontrol circuitry 1002 to allow the pulse generator 1000 to communicatewith an external controller 1080. In one embodiment, the electroniccommunication circuitry 1070 includes a data receiver and a datatransmitter to send and receive and transmit signals and cardiac data toand from the external programmer 1080. In one embodiment, the datareceiver and the data transmitter include a wire loop antenna 1090 toestablish a radio frequency telemetric link, as is known in the art, toreceive and transmit signals and data to and from the externalcontroller 1080.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. For example, the present invention can be used with avariety of medical devices. Additionally, the Figures showing theexemplary embodiments herein are not to scale. Although the use of thelead has been described for use in a cardiac pacing system, the leadcould also be applied to other types of body stimulating systems. Thescope of the invention should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled.

1. An implantable pulse generator, comprising: a signal sensor to sensea first cardiac signal; a blanking window initiator coupled to thesignal sensor, the blanking window initiator adapted to detect andidentify a cardiac event in the first cardiac signal, adjust a blankinginterval using an identified nature of the cardiac event, and start ablanking interval in response to the detection of the cardiac event, theblanking interval including a repeatable noise window blanking interval;and a noise detector coupled to the signal sensor and the blankingwindow initiator, the noise detector adapted to analyze the firstcardiac signal to detect noise in the first cardiac signal during therepeatable noise window blanking interval, wherein the blanking windowinitiator is adapted to repeat the repeatable noise window blankinginterval in response to the detection of noise in the first cardiacsignal during the repeatable noise window blanking interval.
 2. Theimplantable pulse generator of claim 1, wherein the noise detector isadapted to analyze the first cardiac signal to detect noise identifiedby a programmed frequency range.
 3. The implantable pulse generator ofclaim 1, further comprising a pace output circuit to deliver pacingpulses, wherein the blanking window initiator is adapted to identifysensed cardiac events and paced cardiac events and adjust the blankinginterval to a first overall duration if the cardiac event is identifiedas the paced cardiac event and to a second overall duration if thecardiac event is identified as the sensed cardiac event, the secondoverall duration different from the fist overall duration.
 4. Theimplantable pulse generator of claim 3, wherein the blanking windowinitiator is adapted to end the repeatable noise window blankinginterval concurrently with the first overall duration of the blankinginterval if the cardiac event is identified as the paced cardiac event.5. The implantable pulse generator of claim 4, wherein the secondoverall duration includes a first timed interval, and wherein theblanking window initiator is adapted to start the repeatable noisewindow blanking interval after the first timed interval of the secondoverall duration if the cardiac event is identified as the sensedcardiac event.
 6. The implantable pulse generator of claim 1, furthercomprising a pace output circuit adapted to deliver pacing pulsesseparated by a pacing escape interval, and wherein the noise detector isadapted to sum the repeated repeatable noise window blanking intervalsduring the blanking interval and issue a first signal to start deliveryof asynchronous pacing pulses when the sum of the repeated repeatablenoise window blanking intervals is greater than the pacing escapeinterval.
 7. The implantable pulse generator of claim 6, wherein thenoise detector is adapted to issue a second signal to stop the deliveryof asynchronous pacing pulses after the noise is not detected.
 8. Theimplantable pulse generator of claim 1, further comprising a pace outputcircuit adapted to deliver pacing pulses separated by a pacing escapeinterval, and wherein the noise detector is adapted to sum the repeatedrepeatable noise window blanking intervals during the blanking interval,compare the sum of the repeatable noise window blanking intervals to thepacing escape interval, and repeat the pace escape interval when the sumof the repeatable noise window blanking intervals is greater than thepacing escape interval.
 9. The implantable pulse generator of claim 8,wherein the noise detector is adapted to issue a first signal to resumethe delivery of pacing pulses after one pacing escape interval after thenoise is not detected.
 10. A method for operating an implantable pulsegenerator, the method comprising: sensing a first cardiac signal;detecting a cardiac event in the first cardiac signal; identifying thecardiac event as one of a paced cardiac event and a sensed cardiacevent; starting a blanking interval in response to the detection of thecardiac event, the blanking interval including a repeatable noise windowblanking interval and having a first overall duration if the cardiacevent is identified as the paced cardiac event and a second overallduration if the cardiac event is identified as the sensed cardiac event;detecting noise in the first cardiac signal during the repeatable noisewindow blanking interval; and repeating the repeatable noise windowblanking interval in response to each detection of noise in the firstcardiac signal during the repeatable noise window blanking interval. 11.The method of claim 10, comprising ending the repeatable noise windowblanking interval concurrently with the first overall duration of theblanking interval if the cardiac event is identified as the pacedcardiac event.
 12. The method of claim 10, comprising starting therepeatable noise window blanking interval after a first timed intervalof the second overall duration if the cardiac event is identified as thesensed cardiac event.
 13. The method of claim 10, wherein detecting thenoise comprises detecting a signal having a predetermined frequencyrange.
 14. The method of claim 10, comprising: sensing the first cardiacsignal and a second cardiac signal; and blanking the first cardiacsignal and the second cardiac signal during the blanking interval. 15.The method of claim 14, wherein detecting the noise comprises detectingthe noise in the first cardiac signal and the second cardiac signal. 16.The method of claim 10, comprising: summing the repeated noise windowblanking intervals repeated during the blanking interval; comparing thesum of repeated noise window blanking intervals to a pacing escapeinterval; delivering asynchronous pacing pulses if the sum of therepeated noise window blanking intervals is greater than the pacingescape interval; and stopping the delivery of the asynchronous pacingpulses after the noise ceases to be detected.
 17. The method of claim10, comprising: summing the repeated noise window blanking intervalsrepeated during the blanking interval; comparing the sum of repeatednoise window blanking intervals to a pacing escape interval; repeatingthe pace escape interval if the sum of the repeated noise windowblanking intervals is greater than the pacing escape interval; andresuming the delivery of pacing pulses after one pacing escape intervalafter the noise ceases to be detected.
 18. An implantable pulsegenerator, comprising: means for detecting and identifying a cardiacevent in a cardiac signal; means for starting a blanking interval inresponse to the detection of the cardiac event, the blanking intervalincluding a repeatable noise window blanking interval and having anoverall duration adjusted using an identified nature of the cardiacevent; means for detecting noise in the cardiac signal during therepeatable noise window blanking interval; and means for repeating therepeatable noise window blanking interval in response to each detectionof noise in the cardiac signal during the repeatable noise windowblanking interval.
 19. The implantable pulse generator of claim 18,comprising means for blanking the cardiac signal and a further cardiacsignal during the blanking interval.
 20. The implantable pulse generatorof claim 18, wherein the means for detecting the noise comprises meansfor detecting the noise in the cardiac signal and the further cardiacsignal.